Forest admixture as a strategy for enhancing soil-plant properties under semi-arid mediterranean climate in Western Algeria

Forests in Mediterranean semi-arid regions are increasingly threatened by fires, deforestation, lack of management and the intensified effects of climate change. In Western Algeria, Pinus halepensis and Tetraclinis articulata are common species, yet the ecological benefits of their admixture remain poorly documented. This study investigated whether mixed stands improve soil properties and plant traits compared to monospecific stands. Pure stands of each species and mixed stands (60% P. halepensis /40% T. articulata ) were selected in the Tiaret region (semi-arid climate in Algeria). Soil physicochemical and microbiological parameters were measured and infrared signatures were used to characterize soil organic matter and tree needle phytometabolites. Mixed stands significantly enhanced soil physicochemical properties, as reflected by higher porosity (78.3 vs. 79.5), permeability (50.0 vs. 51.3), and C org /N tot ratio (13.5 vs. 20.1) compared to pure stands. Mixing tree species enhanced respiration but lowered microbial biomass which could be explained by the results found via infrared analyses: soils under mixed forests were enriched in more labile organic matter (polysaccharides), whereas monospecific stands accumulate more recalcitrant compounds. Additionally, P. halepensis needles were significantly longer in mixed stands (7.2 ± 0.9 cm) than in pure stands (6.2 ± 0.9 cm), suggesting improved water and/or nutrient uptake. Species admixture also modified phytometabolite profiles, with an enrichment in flavonoids and phenols in both species, with potential consequences in terms of either allelopathy and/or litter decomposition. Overall, our results demonstrate that mixing P. halepensis and T. articulata enhances soil properties and plant traits, supporting the promotion of mixed forests as a nature-based strategy to improve ecosystem responses in Mediterranean semi-arid environments. • Mixed stands improved soil porosity, permeability and organic matter quality. • FTIR spectra show more labile organic matter in mixed vs. monospecific soils. • Tetraclinis articulata needles in mixed stands have higher flavonoid contents. • Longer needles in mixed stands suggest higher resource uptake potential. • Tree admixture enhances the functioning of Mediterranean semi-arid forests.